In a Long Term Evolution (LTE) system, user equipment (UE) sends a preamble to a base station in a random access process, and after receiving a preamble response message fed back by the base station to the UE, the UE accesses the base station.
The UE needs to send a random access preamble to the base station at a particular transmit power. A process of determining the transmit power for the random access preamble by the UE mainly includes the following two steps:
Step 1: The base station determines control parameters of the transmit power for sending the random access preamble by the UE.
The base station determines the control parameters (which are referred to as random access power control parameters below) of the transmit power for sending the random access preamble by the UE. The control parameters include a preamble-initial-received-target-power (preamble Initial Received Target Power), a power ramping step (power Ramping Step), and the like. The base station may use a system default control parameter, or may use a manually set control parameter.
The base station sends the determined random access power control parameters to the UE by using a system information block (SIB) message.
Step 2: The UE determines the transmit power for the random access preamble according to the random access power control parameters sent by the base station.
After obtaining the random access power control parameters by using the SIB message, the UE calculates the transmit power for the random access preamble according to the control parameters:PPRACH=min{PCMAX,PREAMBLE_RECEIVED_TARGET_POWER+PL} [dBm]where PPRACH represents the transmit power for the random access preamble of the UE, and PRACH represents a physical random access channel (Physical Random Access Channel); PCMAX represents a maximum transmit power of the UE when the UE performs random access in a serving cell; PREAMBLE_RECEIVED_TARGET_POWER represents a preamble target received power; and PL represents a path loss (Path Loss) and PL=PRS−RSRP, where PRS represents a reference signal transmit power, and RSRP is a reference signal received power; and a process of calculating the preamble target received power (PREAMBLE_RECEIVED_TARGET_POWER) is as follows:PREAMBLE_RECEIVED_TARGET_POWER=preamble Initial Received Target Power+DELTA_PREAMBLE+(PREAMBLE_TRANSMISSION_COUNTER−1)*power Ramping Step
where preamble Initial Received Target Power represents the preamble-initial-received-target-power, PREAMBLE_TRANSMISSION_COUNTER represents a number of times of sending a preamble in a random access process, power Ramping Step represents the power ramping step, and DELTA_PREAMBLE represents transmit power offsets in different preamble formats (preamble format), which are defined in Table 1 below:
TABLE 1Preamble formatTransmit power offset(Preamble Format)(DELTA_PREAMBLE)00 dB10 dB2−3 dB 3−3 dB 48 dB
In the prior art, for a control parameter of a transmit power for a random access preamble of UE, regardless of whether a system default value or a manually set value is used, a value of the control parameter is fixed and cannot be adaptively adjusted according to an actual need; as a result, a delay of UE in a random access process is uncontrollable.